Thank you for the answers, the error 500 persists some time, bat now the problem is the slowness of the site. Did you find some problems in the debug information?
I see so many errors on your browsers console like:
Failed to load resource: the server responded with a status of 404 (Not Found)
Could you please try to resolve your issue by deactivating all third-party plugins as well as the default theme to check for any possible conflicts with any of the plugins or themes?
The problem is probably Toolset, because everything happened after the last update, however, it is impossible for me to disable the plugins or theme because error 500 often appears.
Well - 500 server error is should be caused by server and whats causing the issue to check that either we need test site or you should check your server logs.